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  • 1995-1999  (30)
  • 1996  (30)
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  • 1995-1999  (30)
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  • 1
    Electronic Resource
    Electronic Resource
    Induced transient birefringence of a resonantly pumped molecular gas (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 105 (1996), S. 6200-6215 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present a theoretical study of the induced transient birefringence of a low density homogeneous molecular gas in a resonant pump–probe experiment. The molecular coherent state induced by the resonant pump field is described by second-order perturbation theory. The induced birefringence can be detected by a delayed probe pulse propagating through the molecular medium after illumination by the pump pulse. In the case of a nonresonant probe, the birefringence is linearly proportional to the mean value of the electronic polarizability of the molecular gas. The birefringence signal is composed of distinct components due to population change and those of rotational, vibrational, and mixed vibrational–rotational origins. This is demonstrated by numerical simulations on Li2 gas. Moreover, the quantum beats contained in the birefringence, as a function of the time delay between the pump and probe pulses, is dominated by the pure rotational motion. Finally, the birefringence is sensitive to the shape of the applied pump pulse and dependent on the spectral phase of the pump pulse. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.472477
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  • 2
    Electronic Resource
    Electronic Resource
    A general method for constructing multidimensional molecular potential energy surfaces from ab initio calculations (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 104 (1996), S. 2584-2597 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A general interpolation method for constructing smooth molecular potential energy surfaces (PES's) from ab initio data are proposed within the framework of the reproducing kernel Hilbert space and the inverse problem theory. The general expression for an a posteriori error bound of the constructed PES is derived. It is shown that the method yields globally smooth potential energy surfaces that are continuous and possess derivatives up to second order or higher. Moreover, the method is amenable to correct symmetry properties and asymptotic behavior of the molecular system. Finally, the method is generic and can be easily extended from low dimensional problems involving two and three atoms to high dimensional problems involving four or more atoms. Basic properties of the method are illustrated by the construction of a one-dimensional potential energy curve of the He–He van der Waals dimer using the exact quantum Monte Carlo calculations of Anderson et al. [J. Chem. Phys. 99, 345 (1993)], a two-dimensional potential energy surface of the HeCO van der Waals molecule using recent ab initio calculations by Tao et al. [J. Chem. Phys. 101, 8680 (1994)], and a three-dimensional potential energy surface of the H+3 molecular ion using highly accurate ab initio calculations of Röhse et al. [J. Chem. Phys. 101, 2231 (1994)]. In the first two cases the constructed potentials clearly exhibit the correct asymptotic forms, while in the last case the constructed potential energy surface is in excellent agreement with that constructed by Röhse et al. using a low order polynomial fitting procedure. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.470984
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  • 3
    Electronic Resource
    Electronic Resource
    On the generality of optimal control theory for laser-induced control field design (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 105 (1996), S. 1299-1300 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Optimal control theory is argued to be the most general method for designing fields used to induce desired chemical reactions. Other "schemes'' for field design which constrain the field form and introduce limiting dynamical assumptions are shown to be particular solutions of the more general optimal control theory (OCT). © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.471967
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  • 4
    Electronic Resource
    Electronic Resource
    A global H2O potential energy surface for the reaction O(1D)+H2→OH+H (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 105 (1996), S. 10472-10486 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A global, single-valued ground-state H2O potential surface for the reaction O(1D)+H2→OH+H has been constructed from a new set of accurate ab initio data using a general multidimensional interpolation method. The ab initio calculations are of the multireference, configuration interaction variety and were carried out using augmented polarized triple zeta basis sets. The multidimensional method is formulated within the framework of the reproducing kernel Hilbert space theory. The H2O potential is expressed as a many-body sum of a single one-body term, three two-body terms, and a single three-body term. The one-body term is the dissociation energy to the three-atom limit 2H(2S)+O(3P). The two-body terms are two O–H and one H–H adiabatic diatomic potentials of lowest energy. Each diatomic term is obtained by interpolating a discrete set of ab initio data using a one-dimensional, second-order, distancelike reproducing kernel. The three-body term is obtained by interpolating the difference of the H2O ab initio data and the one- and two-body sum by means of a direct product of three one-dimensional reproducing kernels on an optimized regular three-dimensional grid. The H2O potential energy surface is accurate, globally smooth, easy to evaluate, and asymptotically correct. Extensive quasiclassical trajectory calculations based on this new potential energy surface have been performed and compared with the results based on the potential energy surface of Murrell and Carter (MC) and that of Schinke and Lester (SL). Comparisons with recent experimental measurements on total cross sections, isotope effects, rate constants, vibrational, rotational, and angular distributions of the O(1D)+H2/HD reaction show that the new potential energy surface is a significant improvement over the MC and SL surfaces. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.472977
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  • 5
    Electronic Resource
    Electronic Resource
    Short-range approach to an A+BC collision complex with a contribution of an ionic state A++BC−: Application to A=H (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 104 (1996), S. 551-562 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: An effective quasi-one-electron asymptotic technique is developed for treating the electronic part of A+BC molecular interaction. The theory proceeds from a model of the motion of an electron in the field of A+ and BC. The interaction between the electron and the ion A+ is handled by a Green function technique while the interaction of the electron with BC is modeled by a short-range approach. The theory provides the electronic wave functions, potential surfaces, and transition dipole moments as functions of three nuclear coordinates specifying the geometrical configuration of the A+BC system. Calculations of potential surfaces are carried out for the case in which A is a hydrogen atom. The main advantage of the theory resides in the fact that the full structure of the potential surfaces and that of transition dipole moments are expressed in terms of a few physical parameters. This feature, along with the ease of computation, turns the theory into a convenient tool for solving the electronic part of molecular dynamics problems for many laser assisted collisions and reactions. The theory significantly extends the method proposed earlier [V. S. Dubov, J. Chem. Phys. 97, 7342 (1992)]. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.470851
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  • 6
    Electronic Resource
    Electronic Resource
    Feasibility of using photophoresis to create a concentration gradient of solvated molecules (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 105 (1996), S. 9515-9524 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The objective of this work is to estimate the feasibility of creating a measurable concentration gradient of molecules in a solvent by a laser driven photophoresis process. The molecules are dissolved in a suitable solvent that is not significantly absorbing at the applied radiation frequency. The molecule is anisotropic, or ideally propeller shaped, and has an appropriate transition dipole capable of driving rovibrational motion. The polarization of the laser can be taken as rotating slowly with the molecules. The resulting torque driven hindered rotation imparts a forward thrust, and thus creates a net flow of the molecules which can set up a concentration gradient in a finite cell. The relevant physical parameters are estimated with the aid of instantaneous normal mode and molecular dynamics simulation methods on a prototype system, and the results indicate that a detectable concentration gradient may be established. A practical issue is to treat heating and resultant mixing or turbulence in the medium. Laboratory experiments are needed to further explore the photophoresis process. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.472785
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  • 7
    Electronic Resource
    Electronic Resource
    A special singular perturbation method for kinetic model reduction: With application to an H2/O2 oxidation model (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 105 (1996), S. 4065-4075 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: An evolution of a homogeneous chemical reaction system is described by a set of nonlinear ordinary differential equations. When the evolution occurs on different time scales, a special singular perturbation method may be employed to extract the equations for the slow evolution. The resultant equations have a quite simple form and retain high accuracy in the solutions. For illustration, an H2/O2 oxidation model is treated by this method. A general reduced model containing no radicals has been obtained, which can be applied to a wide range of initial conditions and has very good accuracy for the temperature and all the species. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.472279
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  • 8
    Electronic Resource
    Electronic Resource
    Optimal control of population transfer in an optically dense medium (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 104 (1996), S. 1173-1178 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We apply the optimal control technique (OCT) to design an optical pulse pair that controls the population transfer in a medium of three-level atoms. The absorption and reshaping of the controlling pulses by the medium are taken into account. The efficiency of the population transfer is improved significantly compared with designs that do not incorporate pulse absorption and reshaping. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.470777
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  • 9
    Electronic Resource
    Electronic Resource
    Application of an inverse method to the determination of a two-dimensional intermolecular potential energy surface for the Ar–OH(A 2Σ+, v=0) complex from rovibrational spectra (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 104 (1996), S. 1187-1202 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A stable inversion method of determining molecular potentials from a finite number of spectroscopic data is presented. Molecular inverse problems are often underdetermined, unstable, and nonlinear. Specifically, the measured spectra contains only partial information of the sought-after potential and even a small error in the data may cause a large variation in the inverted solution. Moreover, the underlying potential is a complicated nonlinear functional of the spectral data. The inversion algorithm, based on the Tikhonov regularization method, resolves all of the above predicaments and yields accurate sought-after potentials with proper analytic properties. The method is applied to extract two-dimensional Ar–OH(A 2Σ+, v=0) potential energy surfaces from the rotational–vibrational spectral data. Two versions of the recovered potential energy surfaces are obtained using two slightly different sets of rovibrational data. These two potentials are basically equivalent, except in the regions to which the data are insensitive, and possess physically acceptable smooth features with the correct long-range behavior. Both recovered potentials reproduce the observed spectra, the estimated rotational constants, and the binding energy within the experimental accuracy. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.470779
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  • 10
    Electronic Resource
    Electronic Resource
    A simplified approach to optimally controlled quantum dynamics (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 104 (1996), S. 4031-4040 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A new formalism for the optimal control of quantum mechanical physical observables is presented. This approach is based on an analogous classical control technique reported previously [J. Botina, H. Rabitz, and N. Rahman, J. Chem. Phys. 102, 226 (1995)]. Quantum Lagrange multiplier functions are used to preserve a chosen subset of the observable dynamics of interest. As a result, a corresponding small set of Lagrange multipliers needs to be calculated and they are only a function of time. This is a considerable simplification over traditional quantum optimal control theory [S. Shi and H. Rabitz, Comp. Phys. Comm. 63, 71 (1991)]. The success of the new approach is based on taking advantage of the multiplicity of solutions to virtually any problem of quantum control to meet a physical objective. A family of such simplified formulations is introduced and numerically tested. Results are presented for these algorithms and compared with previous reported work on a model problem for selective unimolecular reaction induced by an external optical electric field. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.471215
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